The present invention relates to a method for fabricating a thin film transistor, a display device having a circuit using a thin film transistor fabricated by the fabrication method, and a method for fabricating the display device.
As a display panel of a flat panel display device (FPD), a system-in-panel is in practical use in which not only a pixel section but a peripheral circuit including a drive circuit are built on a substrate that forms the display panel. To achieve such a system-in-panel, it is desirable to use a polycrystalline silicon (Si) layer (referred to as a polysilicon layer, a p-Si layer, an ELA silicon layer or the like) for a low-performance thin film transistor (TFT) circuit section, such as a pixel circuit section, which does not need relatively fast operation, while stripe-shaped silicon crystal (also referred to as pseudo single crystal, a laterally grown silicon crystal layer, a SELAX (Selectively Enlarging Laser X′tallization) silicon layer or the like) for a high-performance TFT circuit section, such as a signal line drive circuit, which needs relatively fast operation.
An ELA silicon layer is a particulate polycrystalline silicon layer obtained by applying an excimer laser beam to an amorphous silicon layer (a-Si layer) followed by annealing. This particulate polycrystalline silicon layer is hereinafter also referred to as the ELA silicon layer (ELA-Si) described above. A SELAX silicon layer is obtained by scanning and applying a continuous-wave laser beam to an amorphous silicon layer or an ELA silicon layer to modify it into a silicon layer made of stripe-shaped crystal (pseudo single crystal) grown along the scan direction (lateral direction). This modified silicon layer is hereinafter also referred to as the SELAX silicon layer (SELAX-Si) described above.
JP-A-2002-222959 and JP-A-2003-124136 disclose related art relevant to formation of stripe-shaped silicon crystal. JP-A-08-116067 focuses attention on the film thickness of silicon that forms an active layer from the viewpoint of OFF current in a thin film transistor.